1. Field of the Invention
This invention relates to a control device for a vehicular power transmitting device. More particularly, it relates to a technology of preventing rotary elements of the vehicular power transmitting device from reaching high-speed rotations during a transition in shifting due to an increased variation in torque generated by an internal combustion engine.
2. Description of the Related Art
In general, a vehicular power transmitting device has been disposed between an internal combustion engine and drive wheels for increasing a torque generated by the internal combustion engine, for transmitting the increased torque to the drive wheels. The vehicular power transmitting device was arranged to perform a shifting based on a shifting diagram formed on a two-dimensional coordinate with parameters related to a vehicle condition such as, for instance, an accelerator-opening, representing a depressing stroke of an accelerator pedal, and a vehicle speed. For instance, Patent Publication 1 (Japanese Patent Application Publication 2005-264762) discloses a control device for a hybrid type power transmitting device, in which a shifting was similarly and properly effectuated based on a shifting diagram that was preliminarily stored.
With the power transmitting devices including the device disclosed in Patent Publication 1, the internal combustion engine was supplied with fuel specified for each engine. Therefore, the internal combustion engine has the generated torque in a minimal variation. Thus, the vehicular power transmitting device has performed a shifting control without encountering an adverse affect caused by the variation in such torque, causing no probability of adversely affecting strength of the vehicular power transmitting device. In recent years, there has been probability of using mixed fuel, containing ethanol, in the internal combustion engine. Thus, the torque generated by the engine upon using mixed fuel had a further increased variation than that of toque generated upon using conventional fuel such as gasoline.
If the internal combustion engine generated increased torque with the use of for instance mixed fuel, rotary elements of the power transmitting device reached high-speed rotating states. This occurred during a transition in the shifting effectuated in the power transmitting device based on the conventional shifting diagram. Thus, there is a probability that durability of the rotary elements may drop. Such an issue occurred not only in the hybrid type power transmitting device disclosed in Patent Publication 1 but also in a power transmitting device, composed of for instance a torque converter and an automatic transmission, which was well known conventionally.